Generally, there are two kinds of winding wheels for a yarn feeder which are fixed tension and variable tension. For the fixed tension winding wheel, the winding wheel has a wheel body, and two ends of outer edge thereof respectively have a plurality of metal pieces secured thereon. Each of the metal pieces has an elastic protruding portion at a middle section thereof which is configured to be abutted by a yarn roll so as to secure a position of the yarn roll. The fixed tension yarn feeder has the advantages of simple structure, low cost and is less likely to damage than the variable tension yarn feeder. However, the fixed tension yarn feeder has its shortcomings that when the winding wheel has excessive tension, the yarn roll is difficult to sleeve in and out of the winding wheel, and, on the contrary, when the winding wheel has insufficient tension, the yarn roll may slip related to the winding wheel so that the yarn extraction cannot be precisely controlled. Therefore, the variable tension yarn feeder becomes more used by manufacturers. The variable tension yarn feeder also has a plurality of metal pieces secured on two ends of the winding wheel. The initial positions of the metal pieces are not protruded, and after the yarn roll sleeves on the winding, the metal pieces are controlled through an oil hydraulic pump so as to control the tension between the winding wheel and the yarn roll.
However, the conventional variable tension yarn feeder is disadvantageous because: (i) the variable tension yarn feeder has complicate structure, and the pipes of the oil hydraulic pump are easily stuck so as to damage the winding wheel; and (ii) the oil hydraulic pump needs additional oil pressure system for control, and after yarn roll is sleeved on the winding wheel, a user still needs to operate the oil pressure system to secure the yarn roll, which is inconvenience for operation. Therefore, there remains a need for a new and improved design for a yarn feeder to overcome the problems presented above.